Stator assembly for single phase induction motor employing aluminum alloy starting winding

ABSTRACT

Stator assembly for a motor includes slotted magnetic core with main and auxiliary windings in core slots. Main winding comprises at least two sections each forming a main pole. Auxiliary winding in form of a starting winding also includes at least two sections forming poles angularly displaced from the main poles. Each starting winding is formed of a material that yields the same motor operating performance as a copper starting winding design with a backlash section and yet is provided with fewer, if any, backlash turns as compared to such copper winding arrangement. Preferred auxiliary winding materials have an electrical conductivity of about 29% IACS (International Annealed Copper Standard), a density of about 0.1 pound per cubic inch, and a specific heat at 25* Centigrade of about 0.2 calories per gram per degree Centigrade. When alloy materials are used, the major alloying material or materials, in terms of percentage by weight of the alloy, comprise a sufficiently large percent of the alloy (by weight) that normal manufacturing and processing variations causing variations in the amount of such alloying material or materials still permit the economical manufacture of an alloy having a desired nominal resistivity.

United States Patent [191 Johnson Nov, 20, 1973 4] STATOR ASSEMBLY FORSINGLE PHASE INDUCTION MOTOR EMPLOYING ALUMINUM ALLOY STARTING WINDING[75] Inventor: John H. Johnson, Holland, Mich.

[73] Assignee: General Electric Company, Fort Wayne, Ind.

[22] Filed: Dec. 20, 1971 [2]] App], No.: 209,673

OTHER PUBLICATIONS Bus Conductor Handbook, Alcoa Aluminum, p. 201, 1957Primary Examiner-D. F. Duggan Attorney-John M. Stoudt et a1.

[5 7 ABSTRACT Stator assembly for a motor includes slotted magnetic corewith main and auxiliary windings in core slots. Main winding comprisesat least two sections each forming a main pole. Auxiliary winding inform of a starting winding also includes at least two sections formingpoles angularly displaced from the main poles. Each starting winding isformed of a material that yields the same motor operating performance asa copper starting winding design with a backlash section and yet isprovided with fewer, if any, backlash turns as compared to such copperwinding arrangement. Preferred auxiliary winding materials have anelectrical conductivity of about 29% IACS (International Annealed CopperStandard), a density of about 0.1 pound per cubic inch, and a specificheat at 25 Centigrade of about 0.2 calories per gram per degreeCentigrade. When alloy materials are used, the major alloying materialor materials, in terms of percentage by weight of the alloy, comprise asufficiently large percent of the alloy (by weight) that normalmanufacturing and processing variations causing variations in the amountof such alloying material or materials still permit the economicalmanufacture of an alloy having a desired nominal resistivity.

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STATOR ASSEMBLY FOR SINGLE PHASE INDUCTION MOTOR EMPLOYING ALUMINUMALLOY STARTING WINDING BACKGROUND OF THE INVENTION This inventionrelates to inductive devices in general and, more particularly, tomotors and stator assemblies for motors for use in applications whereinvarious desirable motor characteristics during starting conditions of amotor are at least partly derived from the characteristics of anauxiliary winding.

Single phase, alternating current induction motors of various typesconventionally include a main (e.g., running) field winding and anauxiliary (e.g., starting) field winding, the two windings beingangularly displaced on a stator core member. Upon energization of thetwo windings, phase displaced currents in the windings result instarting torque for the motor.

In one type of single phase induction motor, referred to as a resistancesplit-phase motor, the main winding is arranged in stator core slots tohave relatively high inductance and relatively low resistance, whereasthe auxiliary winding is arranged to have a relatively low inductanceand relatively high resistance. By preselecting the difference betweenthe resistance-to-reactance ratios of the main and auxiliary windings, adesired phase displacement in winding currents and thus starting torquemay be obtained. With this type of motor, the auxiliary winding isdesirably de-energized when a predetermined operating condition isattained, e.g., when the motor attains a predetermined speed.

In many applications, de-energization of the auxiliary winding iseffected by control means in the form of a centrifugal switch mechanismwhich is directly responsive to the attained speed of the motor. Inother applications other means are used. For example, in hermeticallysealed motor applications, it is desirable to use types of control meansthat are located outside the hermetically sealed motor chamber. 7

One particular type of auxiliary winding circuit control means that hasbeen used heretofore has included a commercially available currentresponsive relay, with the relay coil connected in series with the mainfield winding and with normally open contacts of the relay connected inseries with the auxiliary winding. ln operation, the main windingcurrent during an initial energization interval energizes the relay coiland the relay contacts close, thereby to energize the starting winding.Thereafter, as the motor speed increases from standstill, the mainwinding current is reduced in magnitude and the relay contacts open.Thus, the auxiliary winding is de-energized when the main windingcurrent falls to a predetermined relay dropout current value. This willdesirably occur at a predetermined speed, generally selected to bearound 3,200 rpm. in the case of a two pole motor energized by a 60hertz voltage source.

For a given main winding arrangement, care must be taken to insure thatthe contacts of a given relay will close when the locked rotor currentof the main winding flows through the relay coil; and to insure that themain winding current (and relay coil current) will decrease an amountsufficient to cause the'relay to drop out, i.e., open its contacts, onlyafter the motor has accelerated to a preselected speed. Thus, it isdesirable that the relay drop out only after sufficient time has elapsedto permit the attainment of the preselected speed. In addition, it willbe appreciated that, for a given main winding arrangement and currentrelay, the main winding current at a given speed during startingconditions is a function of (among other things) the reactance of theauxiliary winding. Relay characteristics are also described inco-pending application Ser. No. 56,935 filed July 21, 1970 in the nameof Smith et al. The disclosure of that application is specificallyincorporated herein by reference.

One factor which must be considered in the overall design of aresistance split-phase motor that is to be used with a start relay isthe dropout torque of the motor, i.e., the torque supplied by the motorat the time when the relay drops out, the dropout torque also being afunction of the resistance-to-reactance ratios of the main and auxiliarywindings. It has been determined that the main winding current of aresistance splitphase motor will, in general, cause desirable relayoperation, when the resistance of the effective starting winding turnsis high relative to the resistance of the effective main winding turns.For a specified main winding arrangement, therefore, desirable relayoperation will normally occur when the resistance of the startingwinding circuit is relatively high. However, while relatively highwinding resistances are desirable for relay operation, such highresistance conditions are undesirable for other reasons.

For example, relatively high winding resistances may result inrelatively high temperature rises in the start winding. While hightemperature rises are objectionable in general, they are particularlyobjectionable in those applications where the permissible temperaturerise of a motor winding should be relatively low. One type of suchapplication are those where the winding would be confined in a closedcontainer, e.g., a hermetically sealed enclosure.

It is known that the temperature rise of a motor winding is a functionof (among other things) the current density within the motor windingconductors. It will thus be appreciated that, for a given windingconductor material and a given winding current, a desired increase inwinding resistance may usually not be accomplished by merely decreasingthe diameter of the winding material because of an undesired windingtemperature rise that would result from the increased current density inthe winding conductors.

Still another relationship that should be kept in mind when consideringthe temperature rise of a motor winding is the resistivity, weightdensity, and specific heat of the winding material, in view of the factthat temperature rise or rate of such rise of a conductor is generallyproportional to the product of the current density squared times theresistivity, divided by the product of the weight density and specificheat of the conductor. The temperature rise of a winding is of courseimportant by itself, or when a motor user specifies a maximumtemperature rise or rate of temperature rise that will be acceptable tosuch customer. However, temperature rise may also be important due tothe increasein winding resistance that one normally expects to beassociated with an increase in winding temperature and the correspondingreduction in locked rotor torque that in turn results from increasedstart winding resistance in resistance split-phase motors.

In the early development of the motor art, including the hermetic motorart; both the main and starting windings were formed of copper wire.However, particularly in the case of hermetic motor parts, a startingwinding having a desired number of turns formed of copper wire with asufficiently small diameter to provide a desired resistance forpreferred relay operation would have resulted in an excessive windingtemperature rise. For this reason, external resistors were employed inseries with the starting winding in order to provide a desired highstarting circuit resistance while forming the starting winding per sefrom copper conductors sufficiently large in size so that the windingcurrent density and rise would not exceed acceptable levels. Forexample, some motor users specify that current density should not exceed25,000 or 30,000 amps. per square inch of conductor and a maximumtemperature rise rate of about 13F per second. Other users, on the otherhand, may find current densities of 50,000 or 60,000 amps. per squreinch acceptable.

Later, in order to eliminate the external resistor, attempts were madeto utilize phosphor bronze wire as the starting winding conductor. Intheory, the resistivity and weight density of phosphor bronze materialscould be attained so that a desired high winding circuit resistancecould be attained without an external resistor and so that startingwinding current densities and temperature rise would remain withinacceptable limits. For example phosphor bronze having a by weight coppercontent of about 98.75 percent copper and a by weight tin content ofabout 1.25 percent would have a conductivity of about 44% that ofcommercial copper electrical conductors; a weight density of about 8.89gms/cc (about 0.321 lbs/in and a specific heat at about 25C of about0.09 cal/C/gm (about 170.9 joules/C/lb).

However, it will be understood that use of phosphor bronze wire wouldadd appreciably to the cost of a motor because of the cost of thematerial. For example, one pound of the alloy would contain about 0.99of a pound of copper. In addition, the resistivity of 1.25 percentphosphor bronze wire is known to vary to such an extent from lot to lot,that it would be necessary to vary the diameter of the wire from lot tolot in order to obtain wire having a desired or specified resistance perunit length of wire.

It will be understood that the necessity of establishing a differentdiameter of wire for each lot of wire, depending on the resistivity ofthe material, would be expensive in practice. Moreover, variations inwire size from one lot to another would be troublesome to motormanufacturers who design motors so that core slots will have a desiredwinding space factor and who utilize winding generating and handlingequipment whose sat isfactory operation under a given set of conditionswould be more consistent with a single, predictable, wire diameter.

For these and other reasons, a backlash winding rather than a phosphorbronze approach has been used extensively in practice. The generalbacklash approach that was first adopted is still followed today.

By way of background, a backlash winding provides a motor designengineer with a technique of obtaining an essentially continuouslyvariable winding resistance for a given number of effective windingturns. In prac.--

tice, the backlash approach involves winding a desired number ofinductive turns and then adding an additional or excess length ofwinding in order to establish a total winding resistance desired for aparticular motor design.

In other words, wire having a sufficiently large diameter to avoidexcessive current densities and temperature rise is employed in asufficient length to provide the desired resistance. The length'of wirein excess of that needed for the desired number of inductive turns isaccommodated in a backlash winding section. The backlash winding sectionincludes equal numbers of forward and reverse turns with the inductanceof the reverse wound turns cancelling out the inductance of the forwardwound turns.

While the backlash winding approach has provided a means of attaining adesired winding resistance and winding temperature rise characteristicfor many years, the approach has been expensive in practice becauselengths of winding material are provided purely for the sake ofincreasing the over-all winding resistance. These extra turns do nototherwise contribute to the motor performance. The backlash techniquethus adds appreciably to the over-all cost of a motor.

In addition, if the backlash winding coils are manually arranged, anoperator must be sure to reversely dispose half of the turns in thebacklash section. On the other hand, if a winding machine is programmedto wind the reverse or backward turns, the machine must come to a haltafter winding all of the forward turns, reverse directions, and thenwind the reversely disposed turns in the backlash section. This also iscostly because of the expense associated with more complex windingequipment and the expense of extra machine and operator time that isrequired due to stopping and reversing the winding direction of thewinding equipment. It will thus be appreciated that it would bedesirable to reduce, if not eliminate, the number of backlash windingturns that have heretofore been considered to be necessary for a givenwinding arrangement in many given motor designs.

Based on economic considerations, e.g., the relative cost of coppervis-a-vis aluminum winding materials, it is expected that thesubstitution of aluminum magnet wire for copper magnet wire for bothmain and auxiliary windings will become increasingly desirable. However,the resistivity (sometimes also called specific resistance) of aluminumis about 2.828 micro-ohm centimeters at 20 Centigrade as compared withabout 1.724 for copper. Thus, about 1.6 times more volume of aluminumwire per unit length must be employed in order to obtain the samewinding resistance as would be obtained with a unit length of copperwire. Thus, for unit lengths of copper and aluminum wire that are eachto have a given resistance, the cross-sectional area of the aluminumwire must be 1.6 times greater than the cross-sectional area of thecopper wire. It will therefore be appreciated that, particularly foraluminum winding motor designs, winding turns in a backlash section(which do not contribute to running performance of a motor) would occupyspace which could otherwise be used to accommodate winding turns thatcould contribute to the running performance of the motor.

US. Pat. No. 3,348,183 to Ralph E. Hodges and Francisco C. Avila,assigned to the same assignee as the present application, discloses,inter alia, a method of compacting an insulated coil formed of enameledaluminum magnet wire, and US. Pat. Nos. 3,515,919 and 3,528,171 to JackA. I-Ioutman, also assigned to the same assignee as the presentapplication, disclose (among other things) a stator assembly for asingle phase induction motor wherein the main winding is formed ofaluminum magnet wire. In these I-Ioutman patents, the main winding coilsshare slots with the auxiliary winding coils and are compacted in orderto accommodate the auxiliary winding coils. This compacting approach haspermitted the accommodation, in many designs, of increased volumes ofaluminim conductor within a given amount of magnetic core slot volume.However, even when following the Hodges et al. and I-loutman teachings,it has not been possible to convert many copper motor designs toaluminum winding designs. At least some of this problem is due to theneed for aluminum backlash windings in such designs.

Thus, in at least some designs wherein aluminum main windings have beenutilized, it has still been necessary to use copper starting windingcoils rather than aluminum because of the lack of available magneticcore slot space or volume. For example, in one existing aluminum mainwinding motor design which has been examined, a copper starting windinghaving a total of 208 turns were used and of the 208 turns, 68 turns (orover 32 percent) of the total turns were the forward and reverse turnsof a backlash winding section. Assuming that the number of turns in thebacklash winding section could be reduced or eliminated, the windingslot space that would then be made available could desirably be utilizedto accommodate the increased volume of an aluminum conductor and resultin a savings due to the change in winding material as well as due to thereduction or elimination of manufacturing costs associated with backlashwinding sections.

It will be understood therefore from the foregoing, that it would begenerally desirable to provide motor winding arrangements for variousmotor part designs wherein the number of winding turns in a backlashwinding section of a wound stator core are reduced, if not eliminated.

In addition, it would be desirable to provide new and improvedarrangements for resistance split-phase motor parts whereby the numberof backlash winding turns, needed for a desired level of operationalperformance whileutilizing copper starting windings, may be reduced (ifnot eliminated) while retaining a nominal starting winding electricalresistance, and temperature rate of rise so that savings associated withreduced or eliminated backlash winding turns may be realized without asacrifice or reduction in motor operational performance.

SUMMARY OF THE INVENTION It is accordingly a general object of thepresent invention to provide an improved winding arrangement for aninductive device.

It is a more specific object of the present invention to provide astator assembly for a dynamoelectric machine wherein desired auxiliarywinding characteristics, consistently attainable heretofore only withthe use of external resistors or backlash windings, may be attained withan uncomplicated winding arrangement wherein backlash winding turns arereduced in number, if not eliminated entirely.

It is another object of the present invention to provide an improvedauxiliary winding arrangement whereby a material, not heretofore used asa dynamoelectric machine conductor, may be utilized in the formation ofdynamoelectric machine auxiliary windings.

Still another object of the present invention is to provide an improvedstator assembly for a resistance splitphase induction motor employing astarting winding formed of an aluminum alloy.

A further object of the invention is to provide an improved statorassembly for a resistance split-phase induction motor wherein thestarting winding comprises a winding material having predeterminedresistivity, weight density, and specific heat characteristics such thata desired level of motor performance may be achieved with fewer turns(if any at all) of winding material in a backlash winding section thanwould be needed for a similar level of motor performance with a copperstarting winding.

In accordance with one preferred form of the invention, a statorassembly is disclosed herein for a two pole resistance split-phaseinduction motor includinga stator formed of a magnetic core having aplurality of closed end winding accommodating slots. Main and auxiliarywindings are disposed in these slots. The main winding comprises twosections each forming a main pole. Each main winding section includes aplurality of coils of progressively greater pitch each having sidesoccupying a different pair of slots. The exemplified auxiliary windingis a starting winding that also comprises two sections forming two polesangularly displaced from the main poles. Each starting winding sectionincludes a plurality of coils of progressively greater pitch each havingsides occupying a different pair of slots. In the illustratedembodiment, the auxiliary winding is a starting winding formed of amaterial that will yield the same performance as a copper startingwinding design with a backlash section and yet is provided with fewer,if any, backlash turns as compared to such copper winding arrangement.In one preferred exemplification, the starting winding has an electricalconductivity of about 29% IACS (International Annealed Copper Standard),a density of about 2.6 grams per cubic centimeter, and a specific heatat 25 Centigrade of about 0.2 calories per gram degree Centigrade. Inthe illustrated embodiment, the starting winding is a non-copper basealloy, the major alloying material or materials, in terms of percentageby weight of the alloy, comprising a sufficiently large percent of thealloy (by weight) that normal manufacturing and processing variationscausing variations in the amount of such alloying material or materialsnonethelss permit the economial manufacture of an alloy having apredictable resistivity of a nominal value. In a preferred aluminumbased alloy winding material, the major alloying material or constituentcomprises between 4 percent and 6 percent (e.g., 4.5 5.6 percent) byweight of the alloy.

In addition to accomplishing the above stated and other objects of theinvention, other unexpected benefits and advantages may also be obtainedwhen utilizing the invention in the exemplified forms. For example,improved winding distributions may be obtained that contribute toincreased locked rotor torque. Moreover, a measurable reduction in dropoff in locked rotor torque because of winding heating may beaccomplished.

The subject matter which I regard as my invention is particularlypointed out and distinctly claimed in the concluding portion of thisspecification. My invention itself, however, both as to its organizationand method of operation, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly schematic end viewshowing a typical two pole, resistance split-phase, alternating currentinduction motor stator assembly and is useful as an aid in describingprior arrangements as well as embodiments of the present invention;

FIG. 2 is a diagram schematically showing the electrical connections ofthe main and starting windings of the stator assembly of FIG. 1 and alsoshowing, within a phantom line enclosure, one arrangement of backlashwindings known and used heretofore;

FIG. 3 is a graph illustrating a locked rotor torque curve for a twopole, resistance split-phase motor incorporating aluminum main windingsand copper starting windings with backlash winding sections; and

FIG. 4 is a locked rotor torque curve of the general type shown in FIG.3, but for a motor embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of thedrawings, there is shown a stator assembly for a two pole, resistancesplitphase, alternating current induction motor. The stator assembly,generally indicated at 10, comprises a stator core member 11 which maybe formed of a plurality of stacked relatively thin laminations ofmagnetic material. Core member 11 includes yoke portion 12 having aplurality of teeth 13 extending radially inwardly therefrom to definewinding slots 14 therebetween, inner ends 15 of teeth 13 mutuallydefining a bore 16 for receiving the usual squirrel cage rotor member(not shown). In the exemplification, the teeth 13 have been shown asbeing equally spaced apart and bounding 24 equally spaced apart andsimilar winding slots 14, but it will be understood that the inventionmay also be practiced with cores made with laminations having what areknown as graded slots or graded teeth and including those havingnonradial teeth, as well as other slot configurations that may bedesired.

A main or running field winding is provided disposed in certainpredetermined slots 14 so as to form two diametrically opposite mainpoles aligned on the axis shown by the dashed line 17. The main windingis divided into two sections 18a and 18b each forming one of the mainpoles. In the assembly 10, each of the main winding sections 18a, 18bcomprises five concentric coils of progressively greater pitchrespectively designated M M M M and M As shown in FIG. 2, main windingsections 18 and 18b are connected in parallel, however, in certainapplications the main winding sections may be serially connected.

Considering main winding section 18a, the sides of the smallest pitchedcoil M respectively occupy a pair of slots 14-2 on opposite sides ofaxis 17 with slots 14-1 therebetween. The sides of main winding coils MM M and M respectively occupy pairs of slots 14-3, 14-4, 14-5 and 14-6.The sides of main winding coils M through M for convenience, arerespectively positioned at the bottoms or closed ends of the pairs ofslots 14-] through 14-6. Thus The main winding coils M, through M, ofthe other main winding section 18b are similarly positioned incorresponding slots 14, as shown in FIG. 1.

An auxiliary or starting field winding is similarly disposed in certainpredetermined slots 14 and forms two diametrically opposite auxiliary orstarting poles aligned about an axis (angularly spaced in quadrature ornon-quadrature relationship to axis 17) shown by dashed line 19. Thestarting winding is divided into two serially connected sections 20a,20b which respectively form the diametrically opposite auxiliary orstarting poles. In the illustrated embodiment, each of the startingwinding sections 20a, 20b comprises four concentric coils ofprogressively greater pitch respectively designated S S S and 8,.

Referring now to starting winding section 20a, the sides of coil S,share the pair of slots 14-4, on opposite sides of axis 19, with thesides of coils M of main winding sections or parts 18a, 18b. The sidesof coil 8, share slots 14-3 with the sides of coils M and the sides ofcoils S share slots 14-2 with the sides of coils M The sides of thelargest pitched coil S, are the sole occupants of the pair of slots14-1, and the sides of coils S S and S are respectively wound or placedover the respective sides of coils M M and M The starting coils 8,through S, of the other starting winding section 20b are similarlypositioned in corresponding slots 14 on the opposite side of stator core11 as shown in FIG. 1.

The side of coils M M and M of main winding sections 18a, 18b whichrespectively share slots with sides of starting winding coils S S and Sare preferably, but not necessarily, pressed back to facilitateaccommodation of the starting winding coil sides. Particularly when themain windings are formed of aluminum wire, it may also be desirable tocompact the main windings prior to placement of the start windings.

Referring additionally to FIG. 2, ends 22 of main winding sections 18a,18b are shown connected to external terminal 23 having coil 24 ofcurrent responsive relay 25 connected in series therewith. Ends 26 ofmain winding sections 18a, 18b are shown connected together at a commonconnection to lead 27 with end 32 of the starting winding section 20b.This common connection is often buried, and common lead 27 may then beused to provide means for making the common connection. End 28 ofstarting winding section 20a is connected to external terminal 29 havingcontacts 30 of relay 25 serially connected therewith.

Although FIG. 2 does not clearly illustrate the fact, it is sometimesnecessary, according to prior practice, to distribute a backlash windingin several slots, i.e., arrange or wind two or more coils (such as coilsS and S, in FIG. 2) so that each will include some forward and backwardturns of a backlash winding section. This is done, for example, whensuch a large number of backlash turns are needed that the outermost coilslots cannot physically accommodate all of the backlash turns.

In a previously known two pole, resistance splitphase, alternatingcurrent induction motor incorporating a main winding formed of 0.0380inch diameter EC (electrical conductor) grade aluminum wire having aresistance of about 3.22 ohms per pole or section, the starting windingwas formed of 0.0179 inch diameter copper wire having a resistance, tothree significant figures, of about 12.6 ohms. Coils M 'M M M.,, and M,of each winding section or pole 18a, 18b, respectively had 34, 50, 50,68, and 68 turns for a total of 270 turns per pole or section. Each ofthe coils 8,, S and S of each starting winding section 20a, 20brespectively had 21, 30, and 34 turns; and coils S, of each startingwinding section 20a, 2012 had 67 forward wound turns and 39 reversewound turns for a total of 106 turns in each of coils S The total numberof turns per starting winding section was thus 191 turns. Of the 106turns in each coil 8,, 78 turns (i.e., 39 forward wound plus 39 reversewound) were backlash turns, leaving 28 net effective turns in coil SThus about 40 percent of each 191 start turns were backlash turns.

The material used in fabricating the stator assembly for this motorincluded about 0.777 pounds of EC aluminum wire in the main winding witha conductor length of about 276 feet per main pole; and about 0.386pounds of copper wire in the auxiliary or starting winding with aconductor length of about 192 feet per pole and a resistance of about12.6 ohms. Main winding resistance per pole was about 3.22 ohms.

This stator assembly, when built into a motor and tested, provided alocked rotor torque curve or trace A as shown in FIG. 3. Using 3 secondsafter beginning the tests as a reference, the maximum locked torque wasabout 11.0 ounce feet; the minimum locked rotor torque was about 8.4ounce feet; the average locked rotor torque was about 9.7 ounce feet.The slope of the lines A-1 and A-2, fittedto trace A in FIG. 3 indicatethat the drop off in locked rotor torque due to heating was about 0.2ounce feet per second. The trace A (as well as trace B to be describedin conjunction with FIG. 4 hereinafter) was made by a test procedureusing a test rotor and pair of test bearings that supported the rotorfor rotation in the bore of the stator assembly under test.

The windings of the stator assembly to be tested were then connected toa conventional nominal 110 volt alternating current source. However, therotor'was restrained from freely rotating because it was connected,through a LeBow solid state torque transducer (as will be understood) tothe output of a 400:1 gear reduction motor with an output speed of 8.8r.p.m. Essentially the only criteria concerning the selection of thegear reduction motor was that it have sufficient torque to restrain thetest rotor so that the test rotor turned at a substantially constantspeed of 8.8 r.p.m.

The output of the torque transducer, which represented a varyingresistance, was then amplified in a conventional manner to provide atime varying d.c. output voltage that thus varied as the output torqueof the rotor varied during each revolution (about 6.82 seconds perrevolution) thereof. Because of the low speed of the rotor, the outputtorque thereof was taken, as will be understood, to be the locked rotortorque thereof.

The time varying d.c. output voltage was then visually displayed on anoscillograph and recorded on an oscillogram as a torque versus timetrace. Traces made in this manner were then used to make FIGS. 3 and 4herein. The same test procedures and conditions were followed; and thesame rotor and bearing system were used to test the motors for which thetrace data of FIGS. 3 and 4 were obtained.

An improved stator assembly embodying the invention was made and builtinto an improved motor that, upon testing, produced a locked rotortorque curve or trace B as shown in FIG. 4. Before considering trace Bin detail, the winding arrangements for this stator assembly andmaterials used therein will first be described. This second improved,stator assembly (embodying the invention in one form) was also wound asa two pole, resistance split-phase alternating current stator and wasdesigned to have, as near as possible, the

same operating and starting (i.e., performance) characteristics as thestator just described. Accordingly, the same core lamination design wasused and the same stack height, i.e., I i inches was used. The bore wasabout 2 inches.

Accordingly, the main winding was formed of 0.0380 inch EC aluminumwire, it being noted that the conductivity of EC aluminum wire is knownto be about 62 percent of the conductivity of the lntemational AnnealedCopper Standard. Thus, EC aluminum is commonly identified as having aconductivity of 62% IACS or as having a relative electrical conductivity(i.e., relative to copper) of 0.62.

The main winding coils in each pole or section 18a, 18b, were formed sothat the coils M,, M M M and M each had, respectively, 28, 43, 57, 67,and turns for a total of 265 turns. About 0.774 pounds of EC aluminumwire was used with a conductor length of about 275 feet per main poleand a resistance of about 3.21 ohms per pole.

However, the starting or auxiliary winding was formed from a materialthat was preselected to have an electrical conductivity, with referenceto IACS of about 0.40 or less and to have what will be referred toherein as a characteristic ratio R of a value described below, where Ris defined by the equation:

In the above equation that defines the ratio R, p is the electricalresistivity of the material at 20C; as expressed in micro-ohmcentimeters. Also, d is the weight density, at 20C, in grams per cubiccentimeter (gm/cc or gm/cm), and C is specific heat, at 25C, of thepreselected material and expressed in the cgs units of calories per gramper degree centigrade (cal/gm C).

For purposes of information, it is noted that electrical conductorcopper (of the type used in the starting winding of the previouslydescribed motor) would have a weight density of about 8.9 gm/cm; aresistivity of about 1.72 X 10* ohm centimeters or 1.72 micro-ohmcentimeters, and a specific heat of about 0.092 cal/- gram C so that thecharacteristic ratio or R for such copper material would be about 2.2.The dimensional units for R may be readily ascertained from the aboveequation as being (micro-ohms) (C) (cm /(cal); but will not be againreferred to herein. It is also noted that EC aluminum would have an Rvalue of about 5 when the resistivity, specific heat, and weight densityare about (in the units referred to above), respectively: 2.78, 0.2, and2.6. It would be generally desirable to preselect starting windingmaterial having a conductivity of about 40% IACS or less and havingphysical and electrical properties such that the characteristic ratio Rfor the material is greater than about 6 or 7, e.g., 6.5; it being notedthat at least one material (copper-clad steel or copper-coated steel)having an R equal to about 6.8 could be useable to advantage in someinductive device applications.

Additional materials will be specifically identifiedhereinafter thathave the desired properties; but, for purposes of exemplification, analuminum alloy material was chosen for which R was calculated to beabout 10.6. The selected conductor material, to be described in moredetail hereinafter, had an electrical conductivity of about 29% IACS AT20C. One commercial source of an aluminum alloy material having thesedesirable characteristics is Aluminum Company of Amer- S S and S of eachstarting winding section 20a, 20b

respectively had 21, 21 and and 33 turns; whereas coils S of eachstarting winding section 20a, 20b respectively had 42 forward turns andsix reverse turns for a total of 48 turns (12 backlash and 36 effective)and a grand total of 123 turns per winding. Compared to the earlierdescribed motor, a startling reduction in backlash turns wasaccomplished since less than 10 percent of the start turns were backlashturns.

About 0.167 pounds of the 5056 alloy material was used in this startingwinding, with a conductor length,

per starting section or pole, of about 118 feet and a resistance ofabout 12.4 ohms. Somewhat surprisingly and unexpectedly, this improvedmotor exhibited improved starting torque characteristics as revealed bytrace or curve B in FIG. 4.

For example, with reference to the three second torque values for curveB, the maximum locked rotor torque again was 11 ounce feet, but theminimum torque was increased to 9.6 ounce feet, the average torqueincreased to 10.3 ounce feet, and the drop off in torque due to heatingwas also improved and only about 0.13 ounce feet per second. Drop off intorque is, of course, important because; in the eventthat a For purposesof clarifying terminology used herein, it should also be noted that whenthe term relative resistivity" is used herein, the term means thereciprocal of the relative conductivity. Also, for ease of conversion ofdimensional units, it is noted that a specific heat of about 0.22cal/gram C is about equivalent to 410 joules/lb C.

It will be noted from the tables presented below that the weight densityand specific heat of the tabulated alloys are generally comparable tothose characteristics of EC aluminum. It will therefore be understoodthat since the selected alloy has a relatively high relative resistivityof 345% lACS (i.e., 1/0.29 IACS), as compared to EC aluminum which has arelative resistivity of about l/0.62 IACS or 162% lACS; alloy wirehaving a larger diameter and thus larger cross-sectional area ascompared to EC aluminum wire will be used. Thus, for a given current thecurrent density would be less in the alloy than in EC aluminum for aspecified or given temperature rise. Therefore, larger diameter andtherefore generally stronger'wire may be used in a starting winding ascompared to an EC aluminum conductor. This in turn can result in variousmanufacturing advantages as will be discussed in more detailhereinafter.

The following Table 1 sets forth, inter alia, some of the properties ofthe aluminum based alloys referred to above and identified by alloynumbers 2219, 5056, 5083, 5356 and 5456 in the Alcoa Aluminum Handbookpublished by Aluminum Company of America in 1959, 1962, and 1967. Itwill, of course, be borne in mind that any material selected, whetherbased on aluminum, copper, steel, tungsten, silver, etc., is to be drawninto relatively thin wire.

TABLE I Electrical conductivity Specific Density (D.) at 20 C. at 20 0.,heat (C Melting range, percent of at 25 C Alloy GlJem. Lb./cu. in.approximate F. IACS caL/gm. C

rotor for a resistance start motor does not start moving when the motoris first energized (e.g., when the rotor is locked or fstalledl), thelocked rotor torqu e will According to the above referenced Alcoapublication, these alloys further have nominal chemical compositions asshown in Table 11 below.

TABLE 11 Percent Alloy Si Fe Cu Mn Mg Cr Zn Ti Other 2219 0.20 0.30".-.5.8 to 6.8-. 0.20 to 0.40-. 0.02 0.10 0.02 to 0.10 0.15 5056 0.300.40--. 0. 4. to 0.20-- 0.10- 0.15 5083 0.40 0.40 0 1. 4. to 0.25-. 0.155356 0.50 Si plus Fe- 0.10-- 0. 4. to 0.20-. 0. 0.15 5456 0.40 Si plusFe 0.10.- 1. 4. to 0.20 0.25".-. 0.20 0.15

In Table 11 above, only the alloying materials are listed. It will beunderstood that aluminum comprised the balance or remainder of eachlisted alloy and that other represented impurities (on a percent byweight basis) or nonanalyzed materials.

It will be recalled that the motor having characteristics shown by curveB exhibited, after three seconds, an increase in minimum torque of about15 percent; an increase in average torque of about 5 percent; and adesirable 36 percent reduction in torque drop off due to heating. Thismotor also, somewhat surprisingly, exhibited a reduced third hannonicdipin the speed torque curve as compared to the motor from which the curveA data was obtained.

A further desirable feature of the alloy material used in theexemplification described above is that its resistance may be expected,with a 90 percent confidence level, to vary not more than about 3percent from lot to lot with the same wire diameter. Thus, it would notbe necessary to vary wire diameter, from lot to lot, in order to providewire having a desired total resistance per unit length of wire. Thisdesirable feature is believed primarily to be due to the fact that thealloying constituents (i.e., non-aluminum constituents) were about 4percent or more of the total alloy on aweight basis and, therefore,probably more readily controlled.

It will be understood that with the use of preselected auxiliary windingmaterial as taught above, backlash turns may be completely eliminated inboth new and at least some existing motor designs; i.e., motors having aspecified winding arrangement..

For example, one existing two pole, resistance splitphase inductionmotor design had an 0.0359 inch diameter EC aluminum main winding with0.563 pounds of conductor arranged in 257 turns per pole with aresistance of 5.78 ohms per pole. Coils M M M M and M, of each mainwinding section or pole had 38, 43, 51, 63, and 62 turns respectively.An 0.0179 inch diameter copper start winding was utilized with 0.352pounds of conductor arranged in 208 turns perpole, and with a resistanceof 11.5 ohms.

Coils S,, S and S had 22, 38, and 54 turns respectively. Coil S in eachpole was provided with a total of 94 turns. Of these, 60 turns wereforward turns and 34 turns were backward turns. Thus, coil 8., had 26net effective turns and 68 backlash section turns.

For purposes of comparison, a stator assembly for a motor embodying oneform of the present invention was then designed to have operatingcharacteristics similar to those of the motor just described and, exceptfor unexpectedly improved characteristics of the type discussedhereinabove with FIG. 4, similar starting characteristics so as toprovide desired start relay characteristics.

The stator assembly so designed employed 0.0359 inch diameter ECaluminum wire for the main winding with 256 turns and a total conductorweight of about 0.563 pounds. The resistance of the main winding was5.78 ohms. The start winding was made of 0.0269 inch diameter 5056aluminum alloy wire with 139 turns per pole, a conductor weight of about0.156 pounds, and a resistance of about 11.6 ohms. Coils M M M M, and Mof each main winding section respectively had 37, 41, 53, 63, and 62turns. The coils 5,, S S and S of each starting winding sectionrespectively had 24, 34, 39, and 42 turns for a total of 139 turns perpole or section. None of these turns were used as backlash windingturns.

By comparison of the materials used in the two stator assemblies justdescribed, it will be appreciated that utilization of the presentinvention can result in extremely large savings, both in amount ofmaterial used, types of material used; as well as in improved windingarrangements.

There are still further advantages resulting from the use of conductormaterial other than EC copper or EC aluminum wire for the startingwindings where such conductor material has a relatively highresistivity. The very substantial reduction in the number of backlashturns (or complete elimination thereof) provides a reduction in theinternally induced start winding voltage. hi duqfi n ashes" stim 9 b 9!v thsa age, about 65 percent. Furthermore, since the diameter of arelatively high resistivity wire will be greater than that of an ECconductor wire that would provide the same total resistance in a givenmotor design, the wire of preselected material would better withstandstresses during manufacturing that might break a smaller diameter wire.In addition, a wire of relatively high resistivity may now be selectedto have a higher tensile strength per diameter increment thanheretofore. In the case of the alloy used in the above describedpreferred exemplification, the tensile strength may be expected to befrom about 44,000 to about 52,000 psi; and this increased strength willpermit the material to be wound at relatively high speeds on automaticequipment and yet withstand the stresses associated with operation of sshsquipmqnt- It should be noted that materials which would beparticularly attractive for use are those that are alloys of well-knownconductive materials (e.g., copper and aluminum), primarily because ofthe relatively economical commercial availability of such conductivematerials. However, other materials, such as copper plated steel, mightalso be selected. Based on investigations that I have made of differentexisting motor designs utilizing conventional start windings withbacklash sections, the material actually selected would preferably havea relative conductivity for those designs of less than about 40% IACS,and, desirably, from about 18% to about 34% IACS. Although a relativeconductivity greater than about 40% lACS may be desirable for someapplications, it should be noted that at least when an aluminum alloymaterial is used, the relative conductivity would be less than that ofEC aluminum, i.e., less than about 60% lACS.

The characteristic ratio R would preferably be greater than thepredetermined number discussed hereinabove. For example, I havedetermined that materials having an R value of 15 or more and alsomeeting the other selection criteria mentioned above may beadvantageously used.

Although the resistivity or specific resistance is used above in thecalculation of the ratio R for preselected materials, it may occur thatthe published or given data concerning a material under considerationwill be expressed in terms of conductivity or in terms of conductivityrelative to copper at 20C. In this event, it will be helpful tp recallthat resistivity may be determined by dividing 1.72 micro-ohmcentimeters by the known value for conductivity at about 20C of thematerial relative to lACS, (expressed in decimal form). Furthermore,when the conductivity is stated in terms of mhos per centimeter, theresistivity (in ohm-centimeters) will be the reciprocal of theconductivity and may then be easily expressed as micro-ohm centimetersto determine the R ratio given above.

Although the invention has been illustrated and described inconnection'with specific exemplifications of single phase motor statorassemblies having a main (or first) and an auxiliary (or second)winding, the polar axes of the windings may be angularly displaced inquadrature or non-quadrature relationship. it will thus be understood bythose skilled in the art that the invention and benefits derivedtherefrom may be incorporated in other types of dynamoelectric machinesor assemblies having other winding arrangements and different numbers ofpoles comprised of one or more coil groups having one or more coilstherein of at least one turn each. In addition, although all of thestator assemblies actually constructed as described hereinabove had abore of about 2.4 inches in diameter and an outer diameter approximatelyin the neighborhood of 4% to 4% inches; assemblies embodying theinvention may be of any selected size.

Moreover, although the invention has been described with extensivereference being made, for purposes of exemplification, to inductivedevices in the fonn of induction motor stator assemblies (e.g., woundstator cores); and although extensive reference has been made to onespecific preselected material for the same reasons; it will beunderstood that the invention may be used to benefit in connection withvarious inductive devices; such as, e.g., thermally responsive relays.Furthermore, various materials, preselected as taught hereinabove may beutilized.

Therefore, while I have shown and described what at present areconsidered to be preferred and alternate embodiments of my invention inaccordance with the Patent Statutes, changes may be made therein withoutactually departing from the true spirit and scope of the invention.Accordingly, I intend to cover in the following claims all suchequivalent variations as fall within the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A stator assembly for a resistance split-phase induction motorincluding a magnetic core having regions for accommodating windingturns, a first winding having turns thereof disposed accommodated by themagnetic core thereby to establish first polar axes, and a secondwinding having turns thereof accommodated by the magnetic core therebyto establish second polar axes angularly displaced from the first polaraxes; at least some of the turns of said second winding comprising aconductor formed from preselected winding material having acharacteristic ratio R greater than about 6.5, where R is determined bythe relationship p/C, d, where: p is the electrical resistivity inmicro-ohm centimeters of the preselected winding material, C,, is thespecific heat in calories per degree Centigrade gram of the preselectedwinding material, and d is the weight density in grams per cm of thepreselected winding material; thereby to at least reduce the number ofbacklash winding turns needed in the second winding to produce a desiredmotor performance.

2. The stator assembly of claim 1 wherein the first and second windingseach comprise a plurality of coils having at least one winding turneach, and wherein the preselected winding material is an alloy ofaluminum that includes an alloying metal that comprises at least about 4percent by weight of the alloy.

3. The stator assembly of claim 1 wherein said first winding comprises aplurality of coils each having at least one winding turn; the secondwinding includes a plurality of winding coils each having at least onewinding turn; and wherein the preselected winding material is an alloyof aluminum.

4. The stator assembly of claim 3 wherein the preselected windingmaterial has an electrical conductivity less than about 40 percent [ACSand includes at least about 4% by weight magnesium.

5. A stator assembly for a dynamoelectric machine comprising a laminatedmagnetic core having coil accommodating regions and a plurality ofwinding turns supported thereon; at least some of said winding turnsbeing formed from a preselected winding material having a characteristicratio R greater than about 6.5 where R is defined by the relationshipp/C d, where: p is the electrical resistivity, in micro-ohm centimetersof the preselected winding material, C, is the specific heat in caloriesper degree Centigrade per gram of the preselected winding material, andd is the weight density in grams per cubic centimeter of the preselectedwinding material; thereby to provide a dynamoelectric machine having atleast some winding turns formed of a relatively high resistivity ascompared to the resistivity of electrical conductor copper.

6. The stator assembly of claim 5 wherein at least some of saidplurality of winding turns are arranged to establish first polar axes;and other ones of said plurality of winding turns establish other polaraxes angularly displaced from the first polar axes; and wherein thepreselected winding material is an alloy of aluminum.

7. The stator assembly of claim 6 wherein the preselected windingmaterial is of a given diameter and the tensile strength of thepreselected winding material is greater than the tensile strength of aconductor formed of EC aluminum and of the same given diameter.

8. A stator assembly for a resistance split-phase induction motor, amagnetic stator core member having a plurality of winding slots formedtherein each having a closed end; a primary field winding comprising atleast two primary poles having a primary polar axis, each primarywinding pole comprising a plurality of coils each having sides occupyinga different pair of said slots at the closed ends thereof; and anauxiliary field winding comprising at least two auxiliary poles eachhaving an auxiliary polar axis angularly displaced from the primarypolar axis; each primary pole comprising a plurality of coils of windingturns and having sides occupying a different pair of said slots; atleast some of the winding turns of the auxiliary being formed of analuminum alloy wire having a nominal electrical conductivity of fromabout 18% IACS to about 40% IACS.

9. The stator assembly of claim 8 wherein the primary pole of the statorassembly is adapted for connection in series circuit relation with acurrent responsive relay arranged to selectively supply excitationcurrent to the auxiliary winding and wherein the auxiliary winding turnsin each auxiliary pole are wound in the same direction.

10. The stator assembly of claim 8 wherein the auxiliary and primarywindings are arranged to be connected in parallel circuit relation; theresistance-to-reactance ratios of the primaiy and auxiliary windings arepreselected to establish phase displaced winding currents in the primaryand auxiliary windings during concurrent excitation of said windings;and wherein the aluminum alloy auxiliary winding turns in each auxiliarywinding pole provide an electrical resistance of a magnitude thereby toreduce the need for auxiliary winding turns arranged in substractingmagnetic relation in an auxiliary pole relative to other auxiliarywinding turns in the same auxiliary pole, when excited, is reduced.

UNI'IED STA'IES PATENT OFFICE CEl-KTIFICA'IE OF CORRECTION Patent3,774,062 I Dated November 20, 1973 InventOi-(S) John H. Johnson It iscertified that error appears in the aboile-i'dent ified patent and thatsaid Letters Patent are hereby corrected as shown below:

column 6, line 44, change 'nonethelss" to -'nonetheless-.

In column 7, line 63, delete "Thus". I

In column 8, line 20," after "starting" insert ---winding--.

In column 10, line 4, after. "1 3/4" insert (one and 'three quarters) gIn column 10, line 5 after "2 3/8". insert (two end threeeighths)-.

' In column 10, line 56, change --R-- to --"R" In column 10, line 65,change "AT to --at--. H In column 11, line ll, delete "and" (secondoccurrence In column 14, line 49 change "tp" to --t'o-- In column 16',line 237, "after "motor" insert -'-the essembly comprising--.

In column 16, v line 39, after "auxiliary" insert ---poles I Signed andsealed this 22nd day-of April 1975.

01;; Attesting Officer and Trademarks 5-15 (SEAL).

Attest: 1 1 1 c. MARSHALL DANN RUTH C. MASON a Commissioner of- Patentsro-mn (s/eq) Patent No.

Dated November 20, 1973 {mental-(s) John H. Johnson A" It is certifiedthat error appears in the aboire-i'dentified patent and that saidLetters Patent are hereby corrected as shown below:

column column column column column column column column colunn columncolumn line line

line

line

line

line

line

line

line

line

quarters)--'.

after "2 3/8" insert (two and tlireeeighths)--.

change R-'- to '-"R"-'-'.

change "AT" to -at-.

delete "and" (second occurrence) change "tp" to-.

after "motor" insert 'the assembly comprising--.

line 39, after "auxiliary" insert --poles-.

Signed and sealed this 22nd day-of April 1975.

(SEAL) Attest:

' RUTH c. MASON Attesting Officer C. MARSHALL DANN Commissioner ofPatents and Trademarks

2. The stator assembly of claim 1 wherein the first and second windingseach comprise a plurality of coils having at least one winding turneach, and wherein the preselected winding material is an alloy ofaluminum that includes an alloying metal that comprises at least about 4percent by weight of the alloy.
 3. The stator assembly of claim 1wherein said first winding comprises a plurality of coils each having atleast one winding turn; the second winding includes a plurality ofwinding coils each having at least one winding turn; and wherein thepreselected winding material is an alloy of aluminum.
 4. The statorassembly of claim 3 wherein the preselected winding material has anelectrical conductivity less than about 40 percent IACS and includes atleast about 4% by weight magnesium.
 5. A stator assembly for adynamoelectric machine comprising a laminated magnetic core having coilaccommodating regions and a plurality of winding turns supportedthereon; at least some of said winding turns being formed from apreselected winding material having a characteristic ratio R greaterthan about 6.5 where R is defined by the relationship Rho /Cp d, where:Rho is the electrical resistivity, in micro-ohm centimeters of thepreselected winding material, Cp is the specific heat in calories perdegree Centigrade per gram of the preselected winding material, and d isthe weight density in grams per cubic centimeter of the preselectedwinding material; thereby to provide a dynamoelectric machine having atleast some winding turns formed of a relatively high resistivity ascompared to the resistivity of electrical conductor copper.
 6. Thestator assembly of claim 5 wherein at least some of said plurality ofwinding turns are arranged to establish first polar axes; and other onesof said plurality of winding turns establish other polar axes angularlydisplaced from the first polar axes; and wherein the preselected windingmaterial is an alloy of aluminum.
 7. The stator assembly of claim 6wherein the preselected winding material is of a given diameter and thetensile strength of the preselected winding material is greater than thetensile strength of a conductor formed of EC aluminum and of the samegiven diameter.
 8. A stator assembly for a resistance split-phaseinduction motor, a magnetic stator core member having a plurality ofwinding slots formed therein each having a closed end; a primary fieldwinding comprising at least two primary poles having a primary polaraxis, each primary winding pole comprising a plurality of coils eachhaving sides occupying a different pair of said slots at the closed endsthereof; and an auxiliary field winding comprising at least twoauxiliary Poles each having an auxiliary polar axis angularly displacedfrom the primary polar axis; each primary pole comprising a plurality ofcoils of winding turns and having sides occupying a different pair ofsaid slots; at least some of the winding turns of the auxiliary beingformed of an aluminum alloy wire having a nominal electricalconductivity of from about 18% IACS to about 40% IACS.
 9. The statorassembly of claim 8 wherein the primary pole of the stator assembly isadapted for connection in series circuit relation with a currentresponsive relay arranged to selectively supply excitation current tothe auxiliary winding and wherein the auxiliary winding turns in eachauxiliary pole are wound in the same direction.
 10. The stator assemblyof claim 8 wherein the auxiliary and primary windings are arranged to beconnected in parallel circuit relation; the resistance-to-reactanceratios of the primary and auxiliary windings are preselected toestablish phase displaced winding currents in the primary and auxiliarywindings during concurrent excitation of said windings; and wherein thealuminum alloy auxiliary winding turns in each auxiliary winding poleprovide an electrical resistance of a magnitude thereby to reduce theneed for auxiliary winding turns arranged in substracting magneticrelation in an auxiliary pole relative to other auxiliary winding turnsin the same auxiliary pole, when excited, is reduced.